This invention relates to a preform for a composite material which is preferably used for resin transfer molding, and to a fiber-reinforced composite material formed by molding the preform.
As a preform material for resin transfer molding, conventionally, a random mat and a swirl mat are used. Furthermore, if high strength and elastic modulus are required, a laminated product formed of a long fiber fabric in which reinforcement fibers are arranged relatively in line and a material formed by stitching the laminated product so as to be engaged, are used. Recently, various preforms for manufacturing a braiding material having an involute shape, three-dimensional fabric, and the like, which have excellent properties, have been developed.
In a composite material which is reinforced by using a laminated product formed of reinforcement fiber fabric such as a plain-woven fabric, satin woven fabric, and the like, since interlaminar debonding caused by an impact or the like considerably depends on toughness of a matrix resin, it is not easy to give interlaminar debonding resistance at a high level to a composite material formed by molding thermosetting resin using resin transfer molding for a matrix resin, wherein it is difficult to improve the toughness of the resin.
A preform formed as a unit by stitching a laminated product by laminating fabric in the direction of thickness shows an effect of inhibiting the interlaminar debonding. However, on the other hand, a special sewing machine is required in order to stitch the three-dimensional laminated fabric, and there is a trade-off (inverse proportion) between improvement of the interlaminar debonding resistance by increasing stitch density in the direction of thickness and strength in the direction of the inside from surfaces of the laminated product.
In the braiding material and the three-dimensional fabric, reinforcement fiber can be arranged in the direction of thickness of the composite material, and therefore, a composite material having excellent properties can be obtained. However, if large structures are to be manufactured, a machine for manufacturing preforms corresponding to the structures must be huge and the cost per unit of preform will be enormous.
Furthermore, in a composite material obtained by laminating and hardening a sheet type intermediate material (prepreg) made of reinforcement fiber impregnated with thermosetting resin, it is known that thermoplastic resin is provided between layers of a laminated product by a method such that a film, particles, fiber, non-woven fabric, and the like formed of thermoplastic resin are provided on surfaces of prepregs or between prepregs during a step of laminating prepregs in order to improve a property of interlaminar debonding resistance. However, in resin transfer molding in which a preform is formed with reinforcement fiber and subsequently, matrix resin is injected, it is necessary to ensure sufficient flow of the matrix resin when the matrix resin is injected. Therefore, the above method for improving interlaminar debonding resistance which is applied for prepregs cannot simply be applied to the resin transfer molding.
An object of the present invention is to provide a preform for a composite material and a composite material formed from the preform, wherein the composite material can be molded by resin transfer molding, having excellent strength and a property of interlaminar debonding resistance.
As a result of diligent research with regard to the preform for a composite material providing a composite material having excellent strength and excellent interlaminar debonding resistance, the present inventors have found that the above object can be achieved by using a laminated product formed of reinforcement fiber in which a thermoplastic resin layer having a space so as not to inhibit liquid resin from flowing therethrough, is provided between layers of the laminated product. The laminated product is preferably used as a preform for resin transfer molding.
That is, the present invention provides a preform for a fiber-reinforced composite material comprising a reinforcing material formed of reinforcement fiber forming layers as a laminated structure and a thermoplastic resin layer having space so as not to inhibit liquid resin from flowing therethrough, provided between the layers.
Furthermore, the present invention provides a fiber-reinforced composite material formed by molding the above preform for a composite material.